Add an option to make leaderboards count unique loves only

[silentsound]

For product launches or other large cross-team initiatives, folks will often include a group Yelp Love link in the announcement email. Since these go out to a large audience, the individuals on that link will immediately jump to the top of the leaderboards. This doesn't quite accurately reflect how many people these individuals helped, though.

Could we add an option, which defaults to off, that makes the leaderboards count unique love messages received/sent so that we can get around the problem from these "mass love" links? It would be good to keep separate total and unique counts so that changing this option doesn't require a full (lengthy) recount.